Nickel Puts the "Spark" into Spark Plugs
THE MAGAZINE DEVOTED TO NICKEL AND ITS APPLICATIONS
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About 70 tonnes of nickel are used each year to make spark plugs for the estimated 56 million new
vehicles manufactured worldwide.
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SPARK PLUGS consist of a center electrode, a ceramic insulator, steel shell and a ground
electrode.
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NICKEL ALLOY N06600 is a popular choice for ground electrodes because it is easily welded, resists
corrosion and erosion, and can withstand high temperatures.
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The amount of nickel in each is only about a quarter of a gram, but 250 million spark plugs are made every year.
By John Milne
Nickel Magazine, November 2004 -- Fuel-burning engines of all types
require a device to ignite the fuel and thus power the engine. The common spark plug has served this purpose
since
the gasoline engine was introduced at the beginning of the 20th century.
The spark plug both ignites the fuel/air mixture in the combustion chamber and removes heat from the combustion chamber.
Spark plugs consist of a center electrode, a porcelain insulator, steel shell and a ground electrode. The center electrode is usually copper with a nickel alloy tip. The side, or "ground," electrode is made of the same nickel alloy, usually N06600.
Spark plugs do not create heat. Heat is a byproduct of the ignition of the fuel/air mix, and the spark plug will remove some of the generated heat. Temperatures at the "nose" of the spark plug in the combustion chamber are in the 870-925°C range. Thus what’s needed is an alloy that can withstand these temperatures, as well as corrosion and erosion from the fuel combustion, to act as electrodes between which the spark occurs.
The popular choice for spark plug electrodes is nickel alloy N06600 (containing 72% nickel ). Many spark plug manufacturers prefer to use their own proprietary alloy of about 90-96% nickel plus chromium, manganese, silicon and in some instances, yttrium. This nickel alloy is usually welded to a copper center core; the electricity travels from the ignition wiring to the bottom shell of the spark plug. In some designs, the nickel alloy electrodes are plated with platinum for enhanced spark plug life.
All variations of nickel alloy are readily weldable and ductile, so forming is easily accomplished, as is the subsequent adjustment of the gap when spark plugs are installed in an engine.
Nickel alloys are an ideal choice for electrodes because they resist corrosion and erosion from the combustion products and can endure the high temperatures generated. In addition, the nickel alloy is a good conductor of electricity and heat.
The actual configuration, and thus size, of the electrodes varies from manufacturer to manufacturer. However, the following approximate figures give some idea of the volume and weight in the production of spark plugs worldwide.
The actual nickel electrodes are usually 1.32 millimetres (mm) in diameter for the center wire and 2.38 x 1.59 mm for the side electrode, which is a flattened wire in ribbon shape. The amount of nickel alloy per spark plug is small, about 0.25 gram. However millions of spark plugs are made each day. Bosch (Germany) alone makes over a million each working day, and it is only one of the many large world-wide manufacturers.
Every year, about 56 million automobiles are produced worldwide, according to the Society of Automotive Analysts, and all require spark plugs. At five spark plugs per vehicle (allowing for 4-, 6- and 8- cylinder engines), the annual requirement is 280 million. Thus use of nickel alloy for spark plugs could be in the range of 70 tonnes a year just for new vehicles. Add to this the very large replacement automotive business and other internal-combustion devices, such as generators, lawn mowers, motor boats, piston engine aircraft, etc. and the total number of spark plugs used annually is huge.
John Milne is a Bethel, Connectecut-based consultant to the Nickel Institute.
PHOTOS: BOSCH
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